Printing hammer



C. J. HELMS PRINTING HAMMER Oct. 18, 1966 2 Sheets-Sheet 1 Filed June 11, 1965 s 5 Wm n ma W 2. m NJ. A

F Q c United States Patent 3,279,362 PRINTING HAMMER Clifford J. Helms, Woodland Hills, Calif., assignor to Data Products Corporation, Culver City, Calif., a corporation of Delaware Filed Jane 11, 1965, Ser. No. 463,263 19 Claims. (Cl. 10193) This invention relates generally to high speed printing apparatus and more particularly to improved impact devices for use therein.

US. Patent 3,172,352 discloses a printing hammer including, in a preferred embodiment, a pair of fiat springs which conduct current to a coil mounted on the hammers shank. It is pointed out therein that such a construction provides a low friction hammer which can be rapidly moved from a rest position to an impact position, i.e. into engagement with a printing drum. (It will be understood throughout that the hammer does not actually engage the printing drum inasmuch as the paper being printed upon and an inked ribbon is at all times disposed between the hammer and the drum.) Inasmuch as it is desirable that the drum rotate continually if high printing speeds are to be achieved, it is important that the travel time of the hammer be minimized if the printed characters are to be aligned. That is, a signal to start the hammer traveling toward the drum must be provided prior to the character on the drum to be printed moving into printing position. If the travel time interval is relatively long, then a small variation in drum speed during this interval will result in the character being struck either prior or subsequent to it reaching its proper printing position. Thus, by reducing the hammers travel time, greater character alignment and a generally improved printing quality can be achieved. In addition to travel time being significant, printing quality is also affected by contact time, i.e. the interval that the shank is actually in contact with the paper and urging it against the drum. If the contact time is excessive, the printed characters will be smeared since the drum is continually rotating. In order to achieve a maximum printing speed, it is also essential that the recovery time of the hammers be minimized so that no time need be wasted between successive actuations of a hammer.

In view of the above, it is an object of the present invention to provide an improved hammer structure which can be operated so as to have lower travel and contact time than heretofore known hammer constructions.

The desire to minimize travel, contact, and recovery time, assuming that other conditions such as the spring constant of the paper, the force applied to the hammer, etc. are fixed, suggests that the mass of the hammer should be minimized. Accordingly, it is an additional object of the present invention to provide a hammer construction which has a low effective mass.

The aforecited patent discloses at least two hammer embodiments, the first utilizing a coil structure which extends substantially equally above and below the hammer shank and the second utilizing a coil structure which extends either above or below the shank. The first embodiment is inherently balanced but requires the provision of both upper and lower magnets to gain full advantage of the coil length. The second embodiment does not require both upper and lower magnets but is unbalanced and therefore requires that additional mass be provided on the shank to balance the overall structure. If the coil and shank combination are not balanced, there is likely to be a reaction on the supporting springs which would tend to collapse them after extended use. As should be apparent from what has been said thus far, the necessity of adding mass is undesirable since it tends to somewhat increase travel and contact time. In view of the foregoing,

it is still an additional object of the present invention to provide a hammer construction in which the reactions on supporting members are minimized.

Briefly, in accordance with the present invention, a printing hammer is provided comprised of a rigid coil structure, carrying an impact tip thereon, which is supported on a pair of flexible conductive members for substantially rotational movement between a rest position and an impact position.

By selecting a geometry such that the forces applied to the impact tip act at the center of percussion with respect to the point about which the coil structure is rotated, the reaction on the supporting members is reduced to substantially zero. In addition, it is shown herein that the effective mass of the hammer acting at the impact tip is minimized when this geometry is employed.

In the preferred embodiment of the invention, the coil housing is supported by first and second fiat spring members which are crossed and coupled to opposite sides of the coil housing. The spring members extend from a supporting block which has a feature thereof, perpendicular first and second rounded surfaces. A positioning block having first and second perpendicular surfaces, each surface having a series of V-grooves formed therein is provided for receiving such supporting blocks. The V- grooves precisely position each supporting block with respect to translation and rotation about the X, Y, and Z axes. A further feature of the invention involves the provision of a plug-in relationship between the supporting and positioning blocks.

In an alternative embodiment of the invention, the coil housing is supported on a pair of torsion bars which are coupled thereto at the center of rotation thereof.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a side sectional view of a preferred embodiment of a printing hammer constructed in accordance with the present invention;

FIGURE 2 is a horizontal sectional view taken substantially along the plane 2-2 of FIGURE 1 illustrating how the supporting blocks are positioned against a positioning block;

FIGURE 3 is a vertical sectional view taken substantially along the plane 33 of FIGURE 1 and illustrating a rear view of a hammer bank including hammers supported from below and suspended from above;

FIGURE 4(a) is a diagram illustrating the generally rotational movement of the hammer of FIGURE 1;

FIGURE 4(b) is a diagrammatic representation of the significant forces acting on a rigid body during impact analogous to the coil housing of FIGURE 1;

FIGURE 5 is a side sectional view of an alternative embodiment of the invention; and

FIGURE 6 is a vertical sectional view taken substantially along the plane 6-6 of FIGURE 5.

Attention is now called to FIGURES 1 through 3 of the drawings which illustrate a high speed line printing apparatus which employs printing hammers constructed and mounted in accordance with the present invention. More particularly, the printing apparatus includes a printing drum 10 which is adapted to continually rotate about an axis through the center thereof. Raised characters (not shown) are formed on the circumferential surface of the drum 10. The characters are arranged in tracks, each track corresponding to a different position on a line to be printed. Thus, if a maximum of 132 characters are to be printed across any one line, the printing drum will preferably have 132 tracks, with each track containing all of the characters that the apparatus is adapted to print.

A bank of printing hammers 12 is provided spaced from the drum 10. The hammer bank 12 usually includes a number of hammers equal to the number of tracks formed on the drum 10. Positioned between the hammer bank 12 and the drum 10 is a printing ribbon 14 and the paper 16 to be printed upon. In the operation of the printing apparatus, the paper 16 is incrementally driven (by means not shown) to each new line position. After the paper .settles into a new line position, a signal is usually provided to control means (not shown) which functions to actuate each hammer just prior to the character it is to print moves into printing position. When the hammer is actuated, it moves from its rest position toward the drum 10 and strikes the paper 16 urging it against the ribbon 14 and against the appropriate character on the drum, thereby printing it on the paper 16. As previously noted, in order to assure good quality printing, both the travel and contact time of the hammers should be minimized as much as possible.

In accordance with the invention, a printing hammer 18 is provided including an electrically conductive coil 20 disposed in a rigid coil housing 22, preferably formed of a lightweight material such as aluminum. The central portion 24 of the coil housing 22 is left open to minimize the mass of the housing. An impact tip 26 is carried on one end of the housing 22.

The housing 22 is supported on a pair of electrically conductive support members 28 and 30 which preferably comprise fiat spring members whose first ends 32 and 34 are secured to opposite sides of the coil housing 22. The second ends 36 and 38 of the support members 28 and 30 respectively are structurally secured to a supporting block 40. As can clearly be seen in FIGURE 1, the supporting members 28 and 30 extend in planes which intersect each other between the supporting blocks 40 and the coil housing 22.

A cavity 42 is defined in the upper surface of the supporting block 40 and an extension 44 of the coil housing 22 extends therein. The extension 44 is attached to the coil housing 22 (and is preferably formed integral therewith) and is provided to add additional mass to the overall structure comprised of the coil housing 22, coil 20, and impact tip 26 in order to lower the center of rotation of the structure for a purpose which will become more readily apparent hereinafter.

A support assembly 46 is provided which carries a plurality of individually adjustable backstops 48 adapted to engage the rear end 50 of the impact tip 26 when the printing hammer is in its rest position. The front end 52 of the impact tip 26 is of course adapted to force the paper 16 against the ribbon 14 and drum 10.

The first ends 32 and 34 of the conductive support members 28 and 30 extend through openings 54 and 56 in the coil housing and are secured therein as by a potting material. The ends 32 and 34 are respectively electrically connected to first and second terminals of the coil 20. The second ends 36 and 38 of the support members 28 and 30 extend into the supporting block 40 and are connected via conductors 58 and 60 to plugs 62 and 64 which extend from the supporting block 4! Both the rear surface 66 and the bottom surface 68 of the supporting block 40 are rounded, as can be best seen in FIGURES 2 and 3 and are respectively received in V- grooves 70 and 72 formed in perpendicular surfaces 74 and 76 of a positioning block 78. The surface 74 of the positioning block 78 defines a plurality of receptacle pairs, each pair comprised of receptacles 80 and 82 adapted to receive plugs 62 andv 64 projecting from a supporting block 40. The plugs 62 and 64 are both electrically and structurally nested within the receptacles 80 and 82. Connecting terminals 84 and 86 extend outwardly from the rear surface 88 of the positioning block 78 and are electrically connected to the conductive material within the receptacles and 82.

The V-grooves 70 and 72 of course precisely position the supporting block and permit easy registration of all of the printing hammers. A receptacle 90 is provided in the positioning block 78 below each of the V-grooves 72 and in alignment with a threaded opening 92 in each of the supporting blocks 40. A screw 94 projects through each opening 90 and is threadedly received in the Opening 92 to fix the supporting block 40 in position.

The positioning block 78 is oriented relative to the drum 10 such that the impact tips 26 are aligned with the center line of the drum. As shown in FIGURE 3, the hammer bank 12 can consist of two sections, the first section comprised of hammers 18 which are supported above a lower positioning block 78 and a second section comprised of hammers 18 depending from an upper positioning block (not shown). Similarly, lower and upper permanent magnet sections 96, 96' are' provided each defining a plurality of gaps 97, 97', each gap adapted to receive one of the hammers 18, 18 therein. The permanent magnets can be arranged substantially as illustrated in US. patent application Serial No. 419,509, filed December 18, 1964 and assigned to the same 'assignee as the present application. However, whereas the permanent magnet banks are illustrated as being two deep in that application inasmuch as the coil projecting from each shank extends above and below the shank so that each hammer utilizes magnets both above and below its shank, in accordance with the present invention the permanent magnet bank need only be one deep since half of the hammers will utilize the lower magnet bank 96 and half of the hammers will utilize the upper magnet bank 96. The magnet banks can be cantilevered from the support assembly 46 as illustrated.

In the operation of the printing hammer 18 illustrated in FIGURES 1 through 3, in order to propel the impact tip 26 against the drum 10, an electrical current must be supplied between terminals 84 and 86. Consequently, a current will flow through the coil 20 and support members 28 and 30 thus resulting in the generation of a first magnetic field which interacts with a second magnetic field produced by the permanent magnets on either side of the coil 20. The interaction will result in a force being applied to the coil 20 which is perpendicular both to the permanent magnet field and the direction of current within the coil 20. Inasmuch as the current flow through the coil 20 is in a vertical direction within the plane of the paper shown in FIGURE 1 and the magnetic field is perpendicular to the plane of the paper, the resulting force on the coil 20 will be horizontally directed within the plane of the paper therefore acting to propel the impact tip 26 against the drum 10.

Attention is now called to FIGURE 4(a) which comprises a motion diagram illustrating that the coil housing 22 exhibits substantially rotational movement about the point 99 defined by the intersection of the support members 28 and 30 when in a rest position. That is, note that the line 100 representing a line on the coil housing 22 between the openings 54 and 56 is horizontally disposed when the hammer is in the rest position. A line perpendicularly bisecting the line 100 will intersect the point 99. When a force is applied to the coil housing 22, it will be forced toward the drum 10 and it can be shown that the members 28 and 30 will flex equally as illustrated to move the line 108 to the position illustrated in dotted lines. The perpendicularly bisecing line dropped from line Will still intersect the point 99. Consequently, it should be clear that the coil housing 22 effectively rotates about this point which will henceforth be referred to as the center of rotation 99.

In order to determine the optimum geometry of the hammer 18, e.g. the optimum distance between the center of rotation 99 and the impact tip 26, in order to minimize contact time, the hammer can be considered to be a rigid body whose motion can be analyzed during impact. Thus, attention is called to FIGURE 4(b) which illustrates the body as a straight line 102 having a center of gravity G and a center of rotation O displaced by a distance F from the center of gravity G. A force F which is the reaction force on the impact tip when it strikes the drum, acts on the body at a distance r from the center of gravity. The distance r is defined by: r =r +-i Tangential and normal reaction forces R and R will be assumed to be acting at the center of rotation 0.

An equation representing the sum of the moments about the center of rotation O can be written as follows:

da: 2 o o where I represents the moment of inertia and dw/dl represents angular acceleration. Also EM --F r and since F can be represented by K-S where K is the spring constant of the paper and S is the distance that spring is compressed, 2M =-K-S-r Inasmuch as the angular movement of the rigid body about the center of rotation 0 will be small, angular and linear distances can be considered equal and thus S can be represented in terms of the angle 6 such that S er Therefore The moment of inertia I,, mk where m is the mass of the body and k is the radius of gyration with respect to the center of rotation 0. It therefore can be shown that It can be recognized that this equation describes an oscillatory motion whose period -r is represented by mic Km Inasmuch as a positive half cycle of this oscillatory motion represents the contact time of the hammer, it can be appreciated that contact time can be minimized by minimizing the oscillatory period which indicates that the efiective mass mk /r must be :minimized. By manipulating the equation for 1, it can be shown that the period is minimized when For small angles v =r w; thus mk do To E TI Q mic (it), 70 Equation 3 can be integrated twice to obtain F -t mk 2 r where t is the travel time and x is the displacement. travel time Thus Therefore, the travel time is also minimized when the efiective mass mk /r is minimized as described by Equation 2.

It will be recognized that Equation 2 describes the center of percussion of the rigid body 102 rotated about point 0. It should of course be appreciated that the reaction forces acting at the center of rotation will be zero if the force F acts at the center of percussion. (See page 464 of Engineering Mechanics by Timoshenko and Young, third edition, McGraw-Hill Book Company, 1951.) Accordingly, if the dimensions of the hammer 18 are chosen such that the impact tip 26 is positioned at the center of percussion with respect to rotation of the body about point 99, the travel and contact time of the hammer will be minimized and the reactive forces on the supporting members will be reduced to substantially zero. With these considerations in mind, it should be realized that alternative structural embodiments can be provided which also have these characteristics. It should also be appreciated that the extension 44 in the embodiment of FIG- URES 1 through 3 has been provided in order to move the center of rotation out of the area of the coil housing 22. This has been done primarily for space considerations however, and the housing 22 could indeed be mounted for rotation about a point contained therein.

Thus, in FIGURES 5 and 6 a coil housing is provided supporting impact tip 112. The extension 44 has been deleted and therefore the required spacing between the impact device 112 and the center of rotation is smaller. Thus, the center of rotation may be defined at point 114 if the impact device 112 is to be positioned at the cen ter of percussion. The coil housing 110 can be rotated about the point 114 by, for example, providing a pair of torsion bars 116 and 118 which extend outwardly from the housing 119 in opposite directions in line with the point 114. In order to utilize the full length of the coil within the housing 110, both an upper magnet pair 120 and a lower magnet pair 122 are provided. In order to provide support for the torsion bars 116, inasmuch as it is only necessary that they be able to exhibit torsional motion about their longitudinal axis, they can be surrounded by rubber or the like 124 for increased stiffness about the other two axes.

From the foregoing, it should be appreciated that improvements in hammers for use in high speed printing apparatus have been disclosed herein which permit both the travel and contact times of the hammers to be minimized. Travel and contact time minimization occurs as a consequence of several factors. Initially, the effective hammer mass is reduced by mounting the hammer for substantially rotational, rather than linear, movement, and particularly by causing impact forces acting on the hammer to act at its center of percussion. As a consequence of this geometry, bearing reaction on the supporting members is reduced to substantially zero. Thus, no unbalance problem exists and consequently magnetic field producing means, e.g. permanent magnets, need only be provided either above or below the hammers impact tip, but not both above and below. Thus, the magnet banks can be only one deep meaning that the impact tip need be no longer than the coil housing. Consequently, the overall hammer mass can be actually reduced over prior art embodiments. Further improvements introduced herein involve the provision of V-grooves on perpendicular surfaces of the positioning block which receive corresponding rounded surfaces of a supporting block together with the provision of plug-in means for electrically and physically coupling the supporting and positioning blocks.

Although only two embodiments of the invention have been shown herein, it is recognized that other structural configurations can be provided which depend on the inventive concepts disclosed and which do not depart from the true scope and spirit of the invention as claimed.

What is claimed is:

1. A hammer construction comprising:

a rigid member including electrically energizable means for generating a first magnetic field;

means supporting said rigid member for substantially rotational movement about a first axis; and

means establishing a second magnetic field adapted to interact with said first magnetic field.

2. The hammer of claim 1 wherein said rigid member includes an impact tip projecting therefrom.

3. The hammer of claim 2 wherein said impact tip is positioned substantially coincident with the center of percussion for said member rotatable about said first axis.

4. The hammer of claim 1 wherein means supporting said rigid member include first and second flexible support members.

5. The hammer of claim 4 wherein said electrically energizable means comprises an electrically conductive coil having first and second terminals; and

wherein said first and second support members are conductive and are respectively connected to said first and second terminals.

6. The hammer of claim 5 wherein said first and second support members comprise substantially flat springs each having first and second ends and secured at their first ends to a supporting block and at their second ends to said rigid member; and

wherein said fiat springs extend in planes intersecting between said supporting block and said rigid member.

7. The hammer of claim 6 wherein said rigid member includes an impact tip projecting therefrom and positioned substantially coincident with the center of percussion for said member rotatable about said first axis.

8. The hammer of claim 5 wherein said first and second support members comprise torsion bars extending from said rigid member in opposite directions substantially coincident with said first axis.

9. In a printing apparatus including a rotating printing drum having tracks of characters thereon and a hammer bank comprised of a plurality of substantially aligned hammers, each including an impact tip and means for individually propelling each of said tips against one of said characters in a different one of said tracks, the improvement comprising:

a plurality of rigid members;

an impact tip attached to each of said rigid members;

and

means mounting each of said rigid members for rotation about a first axis between a rest position and an impact position.

10. The apparatus of claim 9 wherein said mounting means includes first and second support members for each of said rigid members, each support member having first and second ends; and

means securing said first ends to said rigid members.

11. The apparatus of claim 10 including a plurality of supporting blocks; and

means securing the second ends of first and second support members secured to each rigid member to a diflferent one of said supporting blocks.

12. In a printing apparatus including a rotating printing drum having tracks of characters thereon and a hammer bank comprised of a plurality of substantially aligned hammers, each including an impact tip and means for individually propelling each of said tips against one of said characters in a different one of said tracks, the improvement comprising:

a plurality of rigid members;

an impact tip attached to each of said rigid members;

an electrically conductive coil having first and second terminals carried by each of said rigid members;

a plurality of pairs of first and second electrically conductive support members each having first and second ends;

means structurally securing the first ends of each pair of first and second support members to a different one of said rigid members for rotation thereon about a first axis between rest and impact positions;

means respectively electrically connecting said first and second support member first ends to said first and second terminals to thereby permit each of said windings to be energized to generate a first magnetic field; and

means establishing a second magnetic field to interact with each of said first magnetic fields.

13. The apparatus of claim 12 wherein each of said impact tips is positioned on one of said rigid members substantially coincident with the center of percussion thereof.

14. The apparatus of claim 13 including supporting blocks; and

means securing the second ends of each pair of said first and second support members to a different one of said supporting blocks.

15. The apparatus of claim 14 including a positioning block defining a plurality of pairs of spaced receptacles therein;

each of said supporting blocks being provided with pairs of projecting contacts respectively connected to the first and second support members secured thereto; and

means positioning each of said supporting blocks on said positioning block such that the pair of contacts projecting therefrom projects into one of said pairs of receptacles.

16. The apparatus of claim 14- including a positioning block defining a plurality of slots therein; and

means receiving a different one of said supporting blocks in each of said slots.

17. The apparatus of claim 16 wherein each of said slots comprises a V-groove; and

wherein each of said supporting blocks has a rounded surface received in a different one of said V-grooves.

18. The apparatus of claim 14 wherein said positioning block has first and second substantially perpendicular surfaces, each defining a plurality of V-grooves therein; and

wherein each of said supporting blocks has first and second rounded substantially perpendicular surfaces; and

means positioning said first and second surfaces of each of said supporting blocks in said V-grooves defined in said first and second surfaces of said positioning block.

19. Apparatus for registering a plurality of supporting blocks including:

a positioning block having first and second substantially perpendicular surfaces;

said first positioning block surface defining a plurality of spaced V-grooves;

said second positioning block surface defining a plurality of spaced V-grooves aligned with said grooves in said first positioning block surface;

each of said supporting blocks having first and second substantially perpendicular surfaces;

said first and second supporting block surfaces being rounded and being respectively received in aligned V-grooves in said first and second positioning block surfaces.

a plurality of References Cited by the Examiner UNITED STATES PATENTS 3,172,352 3/1965 Helms lO193 ROBERT E. PULFREY, Primary Examiner.

W. F. MCCARTHY, Assistant Examiner. 

1. A HAMMER CONSTRUCTION COMPRISING: A RIGID MEMBER INCLUDING ELECTRICALLY ENERGIZABLE MEANS FOR GENERATING A FIRST MAGNETIC FIELD; MEANS SUPPORTING SAID RIGID MEMBER FOR SUBSTANTIALLY ROTATIONAL MOVEMENT ABOUT A FIRST AXIS; AND MEANS ESTABLISHING A SECOND MAGNETIC FIELD ADAPTED TO INTERACT WITH SAID FIRST MAGNETIC FIELD. 